The use of gasket materials as seals interposed in the joints or connections of various pieces of a flow line system has long been known, and the variety of sizes, shapes and materials used for gasket seals is multitudinous. Indeed, the needs of different flow lines and the demands placed upon seals in different flow line applications require increasing innovation in gasket technology, especially in flow lines of a type designated as critical service, i.e., flow lines serving to convey fluids at elevated pressures and/or temperatures.
The oil and gas production industry provides a ready example of an industry that requires critical service gasket technology due to the pressures and temperatures involved as well as to corrosive forces inherent in the extraction of oil and/or gas and the transportation of the produced oil/gas to refineries, gas plants, etc. The continued need for improved technology for these pipeline systems is three-fold. First, the pipeline systems employed in the oil and gas industry represent a huge capital investment so that the protection against damage of the various components of the system is cost effective. Second, there are high labor costs associated with the repair and maintenance of such pipeline systems where damage due to corrosion or gasket blowout occurs; these costs result from the amount of time involved to repair the system as well as in the expenses often associated where such pipeline systems are in remote geographic locations, as increasingly becoming the case in the oil and gas production industry. Third, and perhaps more significant, is the potential for environmental damage which can occur, especially in remote, pristine environments, should a pipeline system leak due to deteriorated pipeline components or connections therebetween. Such leakage in the presence of an electric field also creates the environmental danger of fire.
Damage to and deterioration of components in a oil and/or gas pipeline system is a problem that has long time been recognized and stems from several forces, including oxidation, chemical breakdown, electrolysis breakdown and mechanical breakdown. Although providing gasket materials which are resistive to normal oxidation and which are strong enough to withstand the mechanical forces in critical service applications must not be under emphasized, nonetheless the principal focus of deterioration of components used in oil and gas production concern destruction or breakdown of metals either by chemical or electrochemical reaction with the production environment. Numerous substances in the production environment serve to stimulate the corrosion process of metal components, for example, carbon dioxide, hydrogen sulfide and saltwater which are all extremely corrosive to the pipe system and extraction components. These corrosive compounds are abundant in the soil and sea extraction environments typically encountered in the hydrocarbon industry. It has for sometime been further recognized that the flow of oil and/or gas through a metal pipeline causes the production of an electrical current, and the discharge of this current accelerates corrosion of the pipeline components and increase fire danger where leakage result. Also, where two dissimilar metals are in electrical communication, a galvanic cell may be produced which accelerates corrosion of the metal components.
As a result of the recognition of the dangers of electric currents in pipeline systems, there have been many types of dielectric gaskets developed for use in the oil industry. Often, such gaskets employ soft dielectric materials either alone or as a lining on a metallic annular disk. Soft dielectric materials are subject to over compression upon installation which itself may result in leakage at the connective joint. The use of harder dielectric materials encounters problems of cracking when over compressed during installation. In either event, in critical service applications, the high pressure of the contained fluid can cause leakage through the dielectric gasket material and, since the electrical insulating capabilities of the dielectric gasket is a direct function of its thickness, such gaskets are vulnerable to blowout due to the high pressures of the contained fluid when thick section dielectric gaskets are employed.
As a result of these problems, a significant improvement in dielectric gaskets is described in U.S. Pat. No. 4,776,600 issued Oct. 11, 1988 to Kohn, and the present invention is intended to be an improvement over the dielectric pipe flange gasket described in that patent. The present invention provides similar advantages of features with a simplified structure from a manufacturing standpoint. In the '600 patent to Kohn, then, a pipeline gasket is shown which is in annular gasket body which is a lamination of a pair of dielectric linings on opposite sides of a metallic disk. Opposite seal grooves are formed through each lining and into the metal disks, and these grooves are dovetail in cross-section. Ring seals, either in the form of O-rings or lip seals, are shown to be received in these dovetail channels. The structure shown in the Kohn patent has been sold for several years and, more than one year prior to the filing of this application, an improved seal constructed of a spring-biased polytetrafluoroethylene ring has replaced the O-rings and lip seals described in the '600 patent. This improved ring seal has an outer face which matches the outer sidewall of the dovetail and is thicker in dimension than the depth of the dovetail channel. Its width, however, is less than the width of the dovetail so that, upon compression, it may deform within the dovetail channel.
While the structure shown in the Kohn '600 patent as well as the improvement in the ring seal described above have offered a dramatic improvement in the isolation gasket industry, there are nonetheless remains the need to produce a gasket of comparable performance at reduced manufacturing costs. The present invention therefore is directed to such an improvement.